Inspection systems with two X-ray scanners in a first stage inspection system

ABSTRACT

This invention is directed towards finding, locating, and confirming threat items and substances. The inspection system is designed to detect objects that are made from, but not limited to, special nuclear materials (“SNM”) and/or high atomic number materials. The system employs advanced image processing techniques to analyze images of an object under inspection (“OUI”), which includes, but is not limited to baggage, parcels, vehicles and cargo, and fluorescence detection.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention relies on U.S. Provisional Patent No. 60/619,339,filed on Oct. 15, 2005, for priority and is a continuation-in-part ofco-pending U.S. patent application Ser. No. 10/910,250, filed on Aug. 3,2004 which is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 10/662,778, filed on Sep. 15, 2003.

FIELD OF THE INVENTION

The present invention relates generally to X-ray based methods andsystems for detection of concealed threats, and threat resolution, andmore specifically to improved methods and systems, for the detection ofconcealed threats, such as explosives. Optionally, the present inventionuses a multiple stage scanning system to process luggage for thedetection of concealed threats.

BACKGROUND OF THE INVENTION

Conventional X-ray systems produce radiographic projection images, whichare then interpreted by an operator. These radiographs are oftendifficult to interpret because objects are superimposed. A trainedoperator must study and interpret each image to render an opinion onwhether or not a target of interest, a threat, is present. With a largenumber of such radiographs to be interpreted, and with the impliedrequirement to keep the number of false alarms low, operator fatigue anddistraction can compromise detection performance.

Advanced technologies, such as dual-energy projection imaging andComputed Tomography (CT), are being used for contraband detection, inaddition to conventional X-ray systems. In dual-energy imaging, theeffective atomic numbers of materials in containers are measured.However, the dual-energy method does not readily allow for thecalculation of the actual atomic number of the concealed ‘threat’itself, but rather yields only an average atomic number that representsthe mix of the various items falling within the X-ray beam path, as thecontents of an actual luggage is composed of different items and rarelyconveniently separated. Thus dual-energy analysis is often confounded.Even if the atomic number of an item could be measured, the precision ofthis measurement would be compromised by X-ray photon noise to theextent that many innocuous items would show the “same” atomic number asmany threat substances, and therefore the atomic number in principlecannot serve as a sufficiently specific classifier for threat versus nothreat.

In X-ray CT cross-sectional images of slices of an object arereconstructed by processing multiple attenuation measurements taken atvarious angles around an object. CT images do not substantially sufferfrom the super-positioning problem present in standard radiographs.However, conventional CT systems take considerable time to performmultiple scans, to capture data, and to reconstruct the images. Thethroughput of CT systems is generally low. Coupled with the size andexpense of CT systems this limitation has hindered CT use inapplications such as baggage inspection where baggage throughput is animportant concern. In addition, CT alarms on critical mass and densityof a threat, but such properties are not unique to explosives. CT basedsystems suffer from high false alarm rate. Any such alarm is then to becleared or confirmed by an operator, again interpreting images, or handsearching.

Apart from X-ray imaging systems, detection systems based on X-raydiffraction, or coherent scatter are also known. Their primary purposeis not to acquire images but to obtain information about the molecularstructure of the substances an object is composed of. The so-calleddiffraction or coherent scatter signature is based on BRAGG reflectionthat is the interference pattern of X-ray light, which develops whenX-rays are reflected by the molecular structure or electron densitydistribution of a substance. The resulting diffraction spectra can beanalyzed to determine the molecular structure of the diffracting object,or at least to recognize similarity with any one of a number of spectra,which have previously been obtained from dangerous substances.

One approach to detecting explosives in luggage was disclosed in Britishpatent No. 2,299,251 in which a device uses Bragg reflection fromcrystal structures to identify crystalline and poly-crystallinesubstances. Substances can be identified because the energy spectrumdistribution of the polychromatic radiation reflected at selected anglesis characteristic of the crystal structure of the substance reflectingthe radiation.

U.S. Pat. Nos. 4,754,469, 4,956,856, 5,008,911, 5,265,144, 5,600,700 and6,054,712 describe methods and devices for examining substances, frombiological tissues to explosives in luggage, by recording the spectra ofcoherent radiation scattered at various angles relative to an incidentbeam direction. U.S. Pat. No. 5,265,144 describes a device usingconcentric detecting rings for recording the radiation scattered atparticular angles. Each of the prior art systems and methods, however,suffer from low processing rates because the scatter interaction crosssections are relatively small and the exposure times required to obtainuseful diffraction spectra are long, in the range of seconds andminutes. For security inspections, equipment performance has to combinehigh detection sensitivity and high threat specificity with highthroughput, at the order of hundreds of bags per hour.

U.S. Pat. No. 5,182,764 discloses an apparatus for detecting concealedobjects, such as explosives, drugs, or other contraband, using CTscanning. To reduce the amount of CT scanning required, a pre-scanningapproach is disclosed. Based upon the pre-scan data, selected locationsfor CT scanning are identified and CT scanning is undertaken at theselected locations. Here, CT scanning is used as the secondary scan.

U.S. Pat. No. 5,642,393, assigned to Vivid Technologies, Inc., discloses“an inspection system for detecting a specific material of interest initems of baggage or packages, comprising: a multi-view X-ray inspectionprobe constructed to employ X-ray radiation transmitted through orscattered from an examined item to identify a suspicious region insidesaid examined item; said multi-view X-ray inspection probe constructedto identify said suspicious region using several examination angles ofsaid transmitted or scattered X-ray radiation, and also constructed toobtain spatial information of said suspicious region and to determine ageometry for subsequent examination; an interface system constructed andarranged to receive from said X-ray inspection probe data providing saidspatial information and said geometry; a directional, material sensitiveprobe connected to and receiving from said interface system said spatialinformation and said geometry; said material sensitive probe constructedto acquire material specific information about said suspicious region byemploying said geometry; and a computer constructed to process saidmaterial specific information to identify presence of said specificmaterial in said suspicious region.”

In addition, various passive systems have been employed to detectexplosives and specific materials in an object. For example, U.S. Pat.No. 5,007,072 discloses “a method of inspecting parcels to detect thepresence of selected crystalline materials in the presence of othercrystalline and noncrystalline materials comprising: generating x-rayradiation from a source; conveying a parcel containing crystalline andnon-crystalline materials to be inspected continuously past the sourceto irradiate the materials with the radiation; detecting radiationscattered by crystalline material within the parcel at a predeterminedangle; and analyzing a spectrum of the detected radiation to detect thepresence of a selected crystalline material on or within the parcel.”

The above systems do not however, effectively detect high atomic number(“High-Z”) materials. Detecting such materials, particularly smuggledspecial nuclear materials (“SNM”) that could potentially be used to makea weapon, is much more complex task. One of the materials of greatestconcern, highly enriched uranium (“HEU”), has a relatively low level ofradioactivity. Plutonium, yet another nuclear weapons grade material,has a higher specific activity and higher energy emissions. However, itcan also be easily shielded by employing a combination of ahigh-atomic-number (“high-Z”) material for shielding gamma rays and alow atomic number (“low-Z”) neutron absorber for shielding the neutronsproduced by spontaneous fission events. Thus, it is very difficult todetect shielded or concealed materials.

Because typical radioactive sources used in a radiological dispersaldevice (“dirty bomb”) are physically very small but have high specificactivities, they must be shielded for safe handling which prevents theirdetection via well-known passive techniques. For example, an industrialCo-60 source may contain 30,000 Ci in pellet form, wherein the totalcombined weight of the pellets is only about 100 grams. Reducing theexposure rate from this source, and as a result, below the detectionlimits of portal monitors requires a lead shield that is about 40 cmthick and weighing about 5,000 kg.

High atomic number (“High-Z”) screening is feasible due to the highabsorption of X-rays and gamma rays by special nuclear materials andgamma-ray shielding materials, such as lead and tungsten. This is aconsequence of their high density and atomic number (specifically, 74for Tungsten, 82 for Lead, 92 for Uranium, and 94 for Plutonium). Thesematerials are not commonly found within the “normal” stream-of-commerce,characterized primarily by goods composed of low atomic number “low-Z”and “intermediate-Z” elements. Low-Z goods include furniture, produce,clothing, liquids, plastics and other items made from constituents whoseatomic numbers range from 5 to 10 (i.e. Carbon to Oxygen).Intermediate-Z goods include machinery, vehicles, and other items madefrom constituents whose atomic numbers range from 13 to 26 (i.e.Aluminum, Steel).

Accordingly, there is still a need for an improved high z material andexplosive threat detection system that captures data through an X-raysystem and utilizes this data to identify threat items in a rapid, yetaccurate, manner. Further, there is a need for a system that is highlythreat specific for reliably and automatically discerning threats frominnocuous materials and items while still being able to process inexcess of 100 bags per hour. Further, there is a need for a system thatutilizes relatively inexpensive industrial components, and does not needspecial support facilities. Additionally, there is a need for a systemthat provides for greater accuracy in utilizing scan data to identify aninspection region and in processing scan data.

SUMMARY OF THE INVENTION

One object of the present invention is to provide for an improvedscanning process having a first stage to pre-select the locations ofpotential threats and a second stage to accurately identify the natureof the threat. The improved scanning process increases throughput bylimiting the detailed inspection to a small fraction of the total bagvolume.

Another object of the invention is to provide for improved processingtechniques performed in association with various scanning systems.Another object of the invention is to provide for a method and system toscreen for relatively small amounts of threat material. Another objectof the invention is to provide for an improved method and system forscreening for explosives in the form of thin sheets.

Another object of the invention is to provide a screening solution atlow cost by utilizing standard industrial components, includingrelatively low cost and rugged industrial X-ray systems and detectorsystems.

Accordingly, one embodiment of the present invention provides anapparatus for identifying an object concealed within a container. Theseobjects may be considered threats, such as an illegal drug, an explosivematerial, or a weapon. The apparatus for identifying an object concealedwithin a container comprises a first stage inspection system having anX-ray scanning system to generate a first set of data, a plurality ofprocessors in data communication with the first stage inspection systemwherein the processors process said first set of data and wherein thefirst set of data is used to identify at least one target region; ameans for positioning an inspection region relative to the target regionwherein an inspection region at least partially physically coincideswith the target region; and a second stage inspection system forgenerating the inspection region wherein the second stage inspectionsystem produces a second set of data having an X-ray signaturecharacteristic and/or fluorescence signature characteristic of thematerial in said inspection region.

Optionally, the apparatus further comprises a bypass conveyor capable ofmoving said object into a secured area without first passing throughsaid second stage inspection system. Optionally, the operator selects aregion based upon an X-ray characteristic. The X-ray characteristic isat least one of mass, degree of attenuation, area, atomic number, size,shape, pattern, or context. The target region can also be identified byhaving a processor execute an algorithm to select a region based uponsaid first set of data. Optionally, the apparatus has a plurality ofX-ray beam projections intersecting the target region at an intersectionarea. The location of the target region is determined by identifying aset of coordinates for the intersection area.

In another embodiment, the present invention is directed towards amethod for identifying an object concealed within a container,comprising the steps of generating a first set of data using a firststage X-ray inspection system; processing said first set of data using aplurality of processors in data communication with the first stageinspection system; identifying at least one target region from saidprocessed first set of data; positioning an inspection region relativeto the target region wherein the inspection region at least partiallyphysically coincides with the target region; generating the inspectionregion through a second stage inspection system; and producing a secondset of data having a X-ray signature characteristic and fluorescencesignature characteristic of the material in the inspection region.

In another embodiment, the present invention comprises a single stageinspection system comprising an X-ray diffraction and fluorescencediffraction system. Contraband, high z or other illegal material locatedwithin a target object is identified using a radiation source by passinga target object into a C-shaped inspection system; directing an X-raybeam from said radiation source toward a target object; detecting adiffraction signal using a diffraction detector head; detecting afluorescence signal using a fluorescence detector head; and identifyingcontraband material using said diffraction signal and said fluorescencesignal. The method can further comprise the steps of: generating animage of said target object; analyzing the image using an algorithm toevaluate regions of objects based upon a threshold level; segmentingsaid image into regions based upon criteria; further inspecting selectedregions satisfying certain criteria to determine their size and shape;comparing said selected regions to threat criteria; and issuing an alarmto an inspector when an object is determined as matching said threatcriteria in said comparing step.

In another embodiment, the present invention is a device for identifyingtarget material located within a target object using a radiation source,comprising a first member having detector electronics and a diffractiondetector head; a second member affixed substantially perpendicularly tothe first member; a third member affixed substantially perpendicularlyto the second member and parallel to the first member, wherein the thirdmember comprises a radiation source for projecting an X-ray beam towardthe target object and comprises a fluorescence detector head; and aconveyor for positioning said target object between said first memberand said second member. The device can operate by detecting adiffraction signal using a diffraction detector head; detecting afluorescence signal using a fluorescence detector head; and identifyingsaid material using said diffraction signal and said fluorescencesignal.

The device comprises at least one processor and display for generatingan image of said target object; at least one processor having softwarefor analyzing the image using an algorithm to evaluate regions ofobjects based upon a threshold level; at least one processor havingsoftware for segmenting said image into regions based upon criteria; atleast one processor having software for directing the device to furtherinspect selected regions satisfying certain criteria to determine theirsize and shape; at least one processor having software for comparingsaid selected regions to threat criteria; and at least one processorhaving software for issuing an alarm to an inspector when an object isdetermined as matching said threat criteria in said comparing step.

Accordingly, one embodiment of the present invention comprises a firststage X ray inspection system that scans a container at a plurality ofprojections to generate a first set of data comprising the attenuationscan data of the container under inspection and a data processing systemin data communication with the first stage inspection system. Theprocessors process the first set of data to generate at least aplurality of image maps of the container, coded in gravimetric density.The images are then subjected to a set of image interpretationalgorithms, also processed by the processors, to identify target regionsin the images and also generate a three dimensional image map of thecontainer to be displayed on a monitor. Since the images are projectedin different direction it is possible to back-project identified targetregions and to locate those targets in system coordinates.

The first stage inspection system therefore locates potential threatitems, regions, and/or areas, based on X-ray images, manual or automaticdetection algorithms, and triangulation. The second stage inspectionsystem then focuses on the identified items, regions, and/or areas toproduce characteristic signatures which are then used to determinewhether a threat is, in fact, present.

In one embodiment, a target region is identified from the imagesgenerated in the first stage inspection system by having an operatorselect a particular region displayed in the images. In a preferredembodiment, the operator directs a cursor, using an interface, such as amouse, to position crosshairs on each of the two images. The twocrosshairs determine a certain location in system coordinates. Theselection for the cross hair location may occur based upon an X-rayimage characteristic, such as the X-ray shadow of an object, seen inboth images. Optionally, the target selection process may be performedelectronically. Target regions are identified from the two images byhaving a processor execute an algorithm to select regions in the images,which correspond to objects or mass accumulations. With the locations ofeach of the two images determined, the coordinates corresponding to thephysical locations of the target region can be determined and used todirect the system, and, in particular, the conveyor.

Once the target region is determined, either through automatic oroperator processing means, a plurality of control commands is producedand used to position, by a multiple-axis motion control system, thesecond stage inspection system such that an inspection region, at leastpartially, coincides with the determined target coordinates. In oneembodiment, the inspection region is positioned relative to the targetregion using a plurality of adjustable apertures that can be physicallymoved. The apertures can be ring-shaped with an adjustable diameter.Optionally, the means for positioning the inspection volume relative tothe target region comprises a motion-controlled conveyor operable tomove in elevation as well as back and forth relative to the second stageinspection system. Optionally, the inspection region can be moved acrossthe conveyor by mounting the second stage inspection system on a C-armwhich is motion controlled to move back and forth across the conveyor,or alternatively by employing a parallel set of fixed linear bearingsand synchronized linear motion to effect the same relative movement.

The second stage inspection system generates an inspection volume inspace and produces a second set of data having an X-ray signature and/orfluorescence signature characteristic of the material in that inspectionvolume. The X-ray signature characteristic is a diffraction pattern,also called scatter spectrum, and an intensity level associated withthat spectrum, and, in addition, a set of dual energy transmissionmeasurements in close proximity to the ray path of the diffractionmeasurement.

The second stage inspection system comprises a source of X-rayradiation. In one embodiment, it comprises an energy dispersivedetector. In another embodiment, it comprises an array of transmissiondetectors. In another embodiment, it comprises an array of fluorescencedetectors. The energy dispersive detector is used to produce a signatureof the material in the inspection region and the array of transmissiondetectors is used to produce data defining at least one of mass, degreeof attenuation, area, and average atomic number, of the material in abeampath. Optionally, the array of transmission detectors is in a ringformation. In a preferred embodiment, the array of transmissiondetectors comprises high energy and low energy detectors. Data generatedfrom the transmission detectors is used to determine a referencespectrum by identifying a spectrum associated with data generated fromboth the high energy detectors and the low energy detectors. Thereference spectrum can be used to correct a diffraction spectrum or tocorrect for beam hardening.

In one embodiment, the present invention comprises a first stageinspection system having a scanning system to generate a first set ofdata; a plurality of processors in data communication with the firststage inspection system wherein the processors process said first set ofdata and wherein the first set of data is used to identify at least onetarget region; a means for positioning an inspection region relative tothe target region wherein an inspection region at least partiallyphysically coincides with the target region; and a second stageinspection system for generating the inspection region wherein thesecond stage inspection system produces a second set of data having anX-ray signature characteristic of the material in said inspection regionand a third set of data having an fluorescence signature characteristicof the material in said inspection region.

Optionally, the second stage inspection system is a C-shaped inspectionsystem. The second stage inspection system comprises at least onediffraction detector head and at least one fluorescence detector head.The apparatus further comprises a bypass conveyor capable of moving saidobject into a secured area without first passing through said secondstage inspection system. An operator selects a region based upon anX-ray characteristic. The X-ray characteristic is at least one of mass,degree of attenuation, area, atomic number, size, shape, pattern, orcontext. The target region is identified by having a processor executean algorithm to select a region based upon said first set of data.

Optionally, a plurality of X-ray beam projections intersects the targetregion at an intersection area, said target region having a location.The location of the target region is determined by identifying a set ofcoordinates for the intersection area. A plurality of control commandsis produced in response to the determination of said location of thetarget region. The inspection region is positioned relative to thetarget region in response to the plurality of control commands using athree-axis control system.

Optionally, the means for positioning said inspection region relative tothe target region includes a plurality of adjustable apertures. Theapertures can be physically moved in the direction of the main beamaxis. The aperture is a ring aperture having an adjustable diameter. Themeans for positioning said inspection region relative to the targetregion comprises a conveyor operable to move in elevation relative tothe second stage inspection system. The means for positioning saidinspection region relative to the target region comprises an apertureand ring aperture. The second stage inspection system comprises aninspection region generation system. The inspection region generationsystem comprises a source of X-ray radiation.

Optionally, the inspection region generation system comprises an energydispersive detector. The energy dispersive detector is used to produce asignature of the material in the inspection region. The inspectionregion generation system comprises a fluorescence detector. Thefluorescence detector is used to produce a signature of the material inthe inspection region. The first set of data is used to identify areference spectrum. The identification of a reference spectrum isachieved by identifying a spectrum associated with said first set ofdata. The reference spectrum is used to correct a diffraction spectrum.The reference spectrum is used to correct for beam hardening. The X-raysignature characteristic is a diffraction pattern. The X-ray signaturecharacteristic is a scatter spectrum. The X-ray signature characteristicis an electronic response signal.

In another embodiment, the present invention is a device for inspectinghigh atomic number material located within a target object using aradiation source, comprising: a first member having detector electronicsand a diffraction detector head; a second member affixed substantiallyperpendicularly to the first member; a third member affixedsubstantially perpendicularly to the second member and parallel to thefirst member, wherein the third member comprises a radiation source forprojecting an X-ray beam toward the target object and comprises afluorescence detector head; and a conveyor for positioning said targetobject between said first member and said second member.

The device operates by detecting a diffraction signal using adiffraction detector head; detecting a fluorescence signal using afluorescence detector head and identifying said high atomic numbermaterial using said diffraction signal and said fluorescence signal.Optionally, the device further comprises at least one processor anddisplay for generating an image of said target object; at least oneprocessor having software for analyzing the image using an algorithm toevaluate regions of objects based upon a threshold level; at least oneprocessor having software for segmenting said image into regions basedupon criteria; at least one processor having software for directing thedevice to further inspect selected regions satisfying certain criteriato determine their size and shape; at least one processor havingsoftware for comparing said selected regions to threat criteria; and atleast one processor having software for issuing an alarm to an inspectorwhen an object is determined as matching said threat criteria in saidcomparing step.

The aforementioned and other embodiments of the present invention shallbe described in greater depth in the drawings and detailed descriptionprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated, as they become better understood by reference to thefollowing Detailed Description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a block diagram depicting the dual stage X-ray scanning systemas used in one embodiment of the present invention;

FIG. 2 is a schematic view of one embodiment of the dual stage X-rayscanning system;

FIG. 3 is a schematic view of one embodiment of an X-ray scanning systemfor the first stage scanning system;

FIG. 4 is a schematic view of one embodiment of the first stage of theX-ray scanning system for identifying a target region;

FIG. 4a depicts exemplary images for identifying the location of an itemwithin a container;

FIG. 5 is a schematic diagram of a cross-section of one embodiment of abeam delivery system for use in a second stage scanning system;

FIG. 6 is a schematic diagram of one embodiment of the components of abeam delivery system mounted to the open ends of a C-arm supportstructure;

FIG. 7 is an exemplary look up source for transmission spectra;

FIG. 8 is a schematic representation of a beam delivery system havingmultiple energy dispersive detectors;

FIG. 9 is a flow diagram depicting one method of practicing the presentinvention;

FIG. 10 is a flow diagram depicting one method of practicing the presentinvention;

FIG. 11 is a schematic illustration of one embodiment of the systemcomponents having fluorescence detection;

FIG. 12 is a schematic diagram of one embodiment of a first stage CTscanning system;

FIG. 13 is a flow diagram depicting another method of practicing thepresent invention;

FIG. 14 is a flow diagram depicting another method of practicing thepresent invention;

FIG. 15 is a detailed illustration of one embodiment of a baggagescanning system of the present invention, further depicting the X-raytube and beam path;

FIG. 16 is a table showing the K-shell fluorescence line energies in keVof a selection of different materials;

FIG. 17 is a graph depicting the “raw” fluorescence spectrum reflectedfrom a high-atomic-number metal or compound; and

FIG. 18 is a graphical depiction of exemplary calibration curves forUranium, Plutonium, Lead, and Steel relating material thickness to theattenuation (pixel) value.

DETAILED DESCRIPTION OF THE INVENTION

The methods and systems described herein are directed towards finding,locating, and confirming threat items and substances. Such threats maycomprise high z materials and explosives such as C4, RDX, Semtex,Seismoplast, PE4, TNT, dynamite, PETN, ANFO among others, as well asother contraband such as drugs. Although the embodiments have beendescribed in the context of a baggage inspection system, it should beevident to persons of ordinary skill in the art that items other thanluggage such as other packages, mail, and cargo-containers, or evenprocessed food stuffs, can also be analyzed and screened or graded andthat the descriptions are exemplary and are not restrictive of theinvention. Further, while the invention is described as a dual-stagesystem and method, any of the processing techniques discussed herein canbe applied to each of the individual scanning stages.

Referring to FIG. 1, a dual stage scanning system 100 comprises conveyorsystems 121, 122 for moving containers, baggage, luggage, or similarobject 105 through a plurality of scanning stages 110, 115. In oneembodiment, dual stage X-ray scanning system 100 comprises a X-rayscanning unit as a first stage 110 and a Substance-Identification Unit(S-I Unit) as a second stage 115. In an exemplary embodiment object 105is, but is not limited to, a piece of baggage and will be described assuch hereinafter. Baggage 105 moves through the two stages via conveyorsystems 121, 122 in the direction of arrow 125 (along the X-axis).Conveyor systems 121,122 are controlled and coordinated by LuggageTransport Sub-systems (LTS) 141, 142, respectively, thus operating thecombined system 100 at a high-duty cycle. Both the first stage andsecond stage further comprise computer processing systems 131 and 132,for respectively receiving and processing, X-ray data signals and smallangle X-ray diffraction spectra and fluorescence spectra of a threatlocation. Optionally, a bypass conveyor belt is provided between thefirst stage 110 and second stage scanning units 115 that enables theobject 105 to be passed through the scanning system without having to befirst inspected by the second stage scanning unit 115. Such a bypass canbe used if the first stage scanning unit 110 indicates that no threatexists, or no suspicious region exists, in the object 105 based on thefirst stage scan.

In one embodiment, first stage 110 is a CT unit or X-ray transmissionunit, generating imaging data, coded in gravimetric density. Computerprocessing system 131 of the first stage 110, generates automatic imageanalysis resulting in, but not limited to, the approximate shape, size,density, weight and, location of potential threats. As the piece ofbaggage 105 is transported into second stage 115 via conveyor system 122along arrow 125, the computer processing system 132 of the S-I Unitreceives a map of the threats. Processing system 132 also receives theimage volume file from the X-ray scanning or CT Unit via suitabletransmission links, such as, but not limited to an Ethernet LAN (LocalArea Network) connection.

The S-I Unit subsequently interprets the map of threats and image volumedata in second stage 115 and reacts by moving its probing beams into theposition best suited for sampling the threat resolution information. Insecond stage 115, based upon its automatic threat resolution algorithm,the S-I Unit provides data to an operator who can manually activate analarm or clear an object, or, based on the data, the system canautomatically clear the objector activate an alarm.

Referring to FIG. 2, a dual stage scanning system 200 comprises ahousing 230, which encompasses a conveyor system 215 for movingcontainers, baggage, luggage, or similar object 210 through a pluralityof scanning stages 250, 255. A sensor system 265 is connected at theentrance to determine when an object being scanned 210 enters the scanfield and communicates with a controller [not shown] to activate ordeactivate an X-ray radiation source, 270, 272, as needed. A lead linedtunnel 280 surrounds the conveyor to reduce radiation leakage outsidethe equipment. At least one radiation source is not expressly depictedin FIG. 2 and would be visible if the system were viewed from theopposite side.

Referring to FIG. 3, the first stage 350, comprises two X-ray camerasheld together by a support structure 320, such as a frame or yoke, forstability. Each camera consists of an X-ray source 370, 371, a X-rayfocusing means, such as a collimating slit comprised of a radio-opaquematerial, for example lead (not shown), and an array of detectors, 300,301. In one embodiment, it is preferred that the detectors areconfigured into a L-shape in order to save space. One of ordinary skillin the art would appreciate that other folded configurations may beacceptable, provided that the detectors are appropriately positionedrelative to the inspection region and X-ray source.

Behind each slit collimator, a thin sheet of X-rays 310 is formed.Within the sheet, a fan of pencil beams can be defined, shown as dashedlines in FIG. 3, by connecting lines between the stationary focus, notshown, and channels in the detector array. Between focus and detector isa tunnel 380 through which the luggage is transported or moved using anymeans known in the art, including, for example, a conveyor 315, thesurface of which is depicted in FIG. 3. Wherever in the system radiationhas to be transmitted from X-ray sources 370, 371 and through the regiondefined by tunnel 380, the conveyor belt support structure as well asthe tunnel has windows constructed from materials essentiallytranslucent to X-rays. The collimating slits and detector arrays areoriented so that the radiation-fans intersect the main conveyor surfacewithin a few degrees of perpendicular relative to the conveyor surface.The two X-ray sources and their fans point in different directions.

In one embodiment, the detector arrays are mounted on printed circuitboards with a vector positioned normal to their surfaces directed to theX-ray focus. An exemplary printed circuit board has a capacity of 64channels, and the boards are physically arranged in Venetian blindconfiguration. The detector arrays consist of linear arrays of siliconphotodiodes that are covered with scintillation material, which produceslight when exposed to X-rays. The light is detected by the photodiodesthat produce corresponding photo current signals. The detectors measureto what degree the X-ray signal has attenuated due to passing through adefined inspection volume. Specifically, the detected data are convertedto digital format, corrected for detector gain and offset, and thenstored. The required processor means may comprise computing hardware,firmware and/or software known to persons of ordinary skill in the art.When a container under inspection is moving through the tunnel andpassing through the X-ray projections, both detector arrays are beingsampled repetitively between 50 and 500 times per second. Displaying theline projections on a monitor renders the projection X-ray image.

While a conventional line scan system could be used as the first stagescanning system, it is preferred to use the system as described herein.More specifically, the present invention provides for the placement ofat least two X-ray sources such that the directions of the X-rayprojections emanating from the sources are mirrored relative to thecentral vertical plane. Therefore, from the perspective of a view alongthe path of conveyance through the first stage scanning system, at leastone X-ray generator is mounted at a five o'clock position and at leastone X-ray generator is mounted at the 7 o'clock position.

One of ordinary skill in the art would appreciate that the first stagescanning system is not limited to the specific embodiments describedabove and that other variations are included within the scope of thisinvention. In one alternative embodiment, detector arrays are expandedfrom a single array to multiple parallel arrays of detectors. In asecond alternative embodiment, X-ray projections are taken usingtwo-dimensional pixelated detector planes, without requiring the use ofa conveyance means. It should be appreciated that, while the presentinvention will be further described using a description of the inventionbased on using the line scan configuration of single stationary foci andsingle line detector arrays in conjunction with a means of conveyance,the present invention includes other systems and methods that generateX-ray projection images and that such systems and methods can be used inthe novel dual stage scanning system disclosed herein.

An alternative embodiment uses dual energy imaging. Dual energy imagingcan be utilized to display an image where materials of a metallicconstituency are suppressed (not displayed) or materials of an organicconstituency are suppressed. Having the ability to selectively displaycertain materials within images helps reduce image clutter. For example,when inspecting containers for masses or explosives, which have littleor no metallic component, the “organic materials only” display ispreferred. The dual energy approach can be further refined toautomatically discriminate between similar materials of higher and lowerrelative atomic numbers, such as between a plastic comprised of morelower atomic number atoms like hydrogen and carbon and a plasticcomprised of more higher atomic number elements like oxygen andnitrogen; or between aluminum (atomic number 13) and steel (atomicnumber 26).

In one embodiment, dual energy data is generated by using an X-ray tubewith extended spectral emission, which is standard, in conjunction witharrays of stacked detectors, where the first detector is positioned todetect more of the lower energy, or so-called softer X-ray photons, andthe second detector is positioned to detect the balance of the energy,namely the higher energy, or so-called harder, photons. The seconddetector is typically positioned behind the first detector. The lowenergy and high energy measurements are combined in a suitable way usinga series of calibration measurements derived from dual energymeasurements taken of identified organic and metallic materials of knownthicknesses and result in the display of images, including organic onlyor metal only images. One of ordinary skill in the art would appreciatethat various dual energy line scan systems are commercially available.

It is preferred to use projection imaging as the first stage scanningstep in this invention. Features shown in the projection images can beused by an operator to make a final decision on whether items identifiedin a container represent a threat of some type. Additionally, by takingprojections from at least two different angles, it is possible totriangulate the location of a potential threat relative to the physicalcoordinates of the system and use those coordinates to perform a morespecific and focused second stage scan. The triangulation processlocalizes certain items that generate features of interest in the imagesand identifies their location in the form of system coordinates.

To perform the triangulation process, the images that form the basis ofthe triangulation process and that are used to identify a target regionare first identified. In one embodiment, the images are analyzed by anoperator who visually and approximately determines a plurality of X-rayimage characteristics, such as degree of attenuation and projected area,associated with mass, atomic number (identified using image colorcoding), and shape. Operators also use contextual information, such asan X-ray opaque organic mass in a transistor radio or a suspiciouslythick suitcase wall. The analytical process is known to those ofordinary skill in the art and includes the interpretation of X-ray imagecharacteristics.

In another embodiment, images are identified by determining the targetregions automatically. For example, where the screening target is a massof plastic explosive, known algorithms, working on dual energy X-rayprojection image data, can be combined to automatically find suchtarget. Examples for such algorithm components include, but are notlimited to, edge detection, watershed, and connected component labeling.

Referring to FIG. 4, a container 110 is moved on a conveyor 115 througha tunnel 180 in x-direction, perpendicular to the plane of the Figure. Afirst X-ray generator 170, C1, with an X-ray emitting focus projects afan of X-rays 300 through a slit collimator onto an array of detectorsmounted on printed circuit boards 200. One of ordinary skill in the artwould appreciate that only a small sampling of detectors are shown inFIG. 4 and that a typical system would have a far greater number ofdetectors, preferably 700 to 800, more preferably 740. As shown, theorientation of the fan plane is perpendicular to the conveyor surface.While a container is being moved along the conveyor surface, thedetectors are read out repeatedly, and their signals are converted intodigital format by detector electronics that are also mounted on thedetector boards 200. The data are being processed and sorted further andstored in a computer [not shown] for display on a monitor [not shown].Each horizontal line on the monitor corresponds to one particulardetector in the array. Therefore, in a system using 740 detectors, thefull image is composed of 740 lines.

A second X-ray camera, C2, consisting of X-ray generator 171, slitcollimator (not shown) and detector array 201 is mounted in a differentorientation, and offset in conveyor direction, by typically 100 mm. Thedetectors aligned with this camera are sampled essentiallysimultaneously with the detectors of the first camera and produce asecond image displayed on a monitor.

Operationally, an item 340 located within the container 110 isrecognized in the course of the first stage scan using a detectionalgorithm or by operator analysis, depending upon the system modechosen. With the item 340 identified, the approximate centerline X-rayprojections 330, 331 that pass through the object can be determined.Each of the centerlines 330, 331 is associated with a certain detectorchannel, 310 and 311 respectively in each view.

Referring to FIG. 4a , once the detector channels have been determined,the location of the associated item 440 can be found in the y-zcoordinate system. Two images 480, 481 corresponding to the two viewsare shown. With knowledge of the detectors associated with thecenterlines 431, 430 and the range of detectors defined, the y and zcoordinates of the item 440 can be derived. The x-coordinate is definedby the direction of conveyor motion and is known because the conveyormotion control system, timing of X-ray exposure, and the fixed offset ofthe two scan planes are known. The x-coordinate can, for example, bereferenced to the beginning, or leading edge of the container, which canbe detected by a light curtain or similar position-detecting device. Inparticular, the two images are referenced to each other precisely in thex-coordinate direction.

The purpose of this triangulation or localization of identified items ina container is to generate control commands that can be used to positionand focus the inspection region or inspection volume of the second stagescanning system on the identified item. Therefore, the first inspectionstage quickly locates potential threats and determines theircoordinates, as referenced to the system, while the second stage focuseson better determining the nature of the identified potential threat. Itshould be appreciated that, because the first stage characterization ofa threat is loosely based on features in X-ray images, it will locate,find, and label, as a potential threat, items which are innocuous, inaddition to real threats. Therefore, the performance of a detectionsystem based only on the first stage, as described, suffers from a highfalse alarm rate.

One of ordinary skill in the art would also appreciate that otherelements of the first stage scanning system are not depicted in FIG. 1but would be included in an implementation of the system. For example, ashielding curtain is positioned at both the entrance and exit of thesystem to protect against radiation leakage to the surroundingenvironment. The system is controlled by a data interface system andcomputer system that is capable of rapid, high data rate processing, isin data communication with storage media for the storage of scan dataand retrieval of reference libraries, and outputs to a monitor having agraphics card capable of presenting images.

It should also be appreciated that a second stage scan may not berequired. In one embodiment, radiographic images from the first stagescan are displayed on a computer monitor for visual inspection withtarget regions or potential threats identified. An operator may dismisssome of the identified regions or threats based on context, observation,or other analytical tools. If no threats are identified, the containeris cleared to exit the inspection system without subjecting it to thesecond stage of scanning. However, if the operator is unable to resolvean area as being a non-threat, the area is identified as a targetregion.

The second stage inspection or scanning system closely inspects theidentified target locations by deriving more specific information, or asignature, and confirming the first stage threat alarm only if theobtained signature matches the signature of a threat substance or threatitem. An alarm confirmed by the second stage system are then takenseriously by operators and indicate the need for further inspection,including, but not limited to, operator image interpretation, additionalscanning, and/or hand searching the container.

In one embodiment, the second stage scanning system uses diffracted orscattered radiation to determine the properties of a material, obtain asignature, and, accordingly, identify a threat. Diffracted or scatteredradiation comprises photons that have experienced an interaction withthe object under investigation. In the special case of small anglescattering, the majority of interactions are elastic orenergy-conserving; specifically, the diffracted photon has the sameenergy as it had before the interaction, just its direction ofpropagation has changed. If the energy distribution of the scatteredphotons is being analyzed by an energy-dispersive detector system, whichis commercially available, certain properties of the material causingthe scatter are being encoded in the signature. Photons scattered undersmall angles are scattered selectively due to interference effects.Since the process does not change the energy of the photons the signalalso contains the distribution of the primary radiation in a simplymultiplicative way. The incoming primary radiation, as well as thescattered radiation, encounter further spectral modifications due toother types of interactions, such as Compton scatter and photoelectricabsorption, which are not energy preserving. If one wants to view thecharacteristics of the scattering material, other distracting spectraleffects have to be removed.

The detected signature of a threat is therefore a combination of X-rayproperties. One important property is a BRAGG diffraction spectrum,observed at small diffraction angles between 2 and 8 degrees, with apreferred value around 3 degrees.

FIG. 5 shows schematically a cross section of a preferred beam deliverysystem used to obtain BRAGG spectra at small angles. Other beam deliverysystems can also be used in the present invention, including thosedisclosed by Kratky, et al. in Austrian Patent No. 2003753 and Hardingin U.S. Pat. No. 5,265,144. The system depicted in FIG. 5 furtherincludes a transmission detector.

A beam delivery system separates the photon radiation emitted by thefocus 500 of the X-ray source 504 into a plurality of beams. A beam 501is formed by passing through apertures 510 and is directly detected bydetectors 502, which are within the beam's direct line-of sight. Thesebeams are referred to as transmission beams. Scatter interactions aredetected by blocking direct line-of-sight detection through the use ofring apertures 510, 511 and exposing the associated detector 520 only toscattered radiation 592. Therefore, scatter radiation, generated whencertain beams interact with an inspection region or volume 545, can bedetected in the same apparatus as transmission radiation.

The choice of ring aperture diameters, distance to focus, and distanceto detector determines the effective scatter angle 430 of the photonsfalling on the detector. In one embodiment, the scatter angle 530 isapproximately the same for substantially all photons detected by thedetector of the scattered radiation. It is preferred to configure thebeam delivery system to establish an effective scatter angle of betweentwo and 8 degrees. It is more preferable to have a scatter angle at orabout 3 degrees. Using a beam delivery system having a circular symmetryhas the advantage of obtaining a scatter contribution from a largervolume of the material being inspected, thereby increasing theinherently weak scatter signal. Additionally, the scatter spectrum canbe cost efficiently detected using only a single detector channel 520with an entrance aperture in the shape of a hole 521.

The scatter signal is generated by positioning the target region 545,identified in the first stage scan, between the beam forming apertures,irradiating that region 545 using the conical beam 542, and making surescatter radiation from the target region 545 can be detected by thescatter detector. The target region 545, often contained within acontainer 550, is in the shape of a tube or ring 545 and is referred toas the inspection volume or inspection region. The length, diameter, andwall thickness of the inspection volume depends on the particular shapeof the elements of the beam delivery system, including focus size, ringaperture diameter and width, detector opening and overall distance. In apreferred embodiment for the inspection of large luggage, the inspectionvolume is at or about 60 cubic centimeters.

In one embodiment, as shown in FIG. 6, the components of the beamdelivery system are mounted to the open ends of a rigid supportstructure 600 formed in the shape of a C (referred to herein as a C-arm)and aligned with a tolerance of at or about 0.1 millimeters. A first armof the C-arm comprises a X-ray tube with X-ray focus 672, a beamlimiting aperture hole mounted to the tube head 601, and a ring-shapedaperture 610. A second arm holds comprises a transmission detector array602, a second ring aperture 611, and an energy dispersive detector 620,equipped with an aperture hole.

The energy dispersive detector 620 is positioned to receive scatteredradiation from a target object placed on the conveyor running betweenthe arms of the C-arm support structure where a first arm is above theconveyor and a second arm is below the conveyor. The transmissiondetector is positioned to receive radiation attenuated by the sametarget object. It is preferable for the C-arm to be mobile and capableof moving in the x-direction along the length of the conveyor.Therefore, the C-arm with tube and detectors can be re-positioned alongthe length of the conveyor.

In a preferred embodiment, the scatter detector 620 is comprised ofcadmium telluride or cadmium zinc telluride and is operated at roomtemperature, or approximate to room temperature, An exemplary embodimentis available from the e-V Products Company, Saxonburg, Pa. This type ofdetector has a spectral resolution performance that is well matched tothe limited angular requirements of this application, and therefore thelimited spectral resolution of the beam delivery system.

In one mode of operation, the potential threat locations inside acontainer are found automatically by the first stage, and, based uponthe physical coordinates obtained through triangulation, the secondstage scanning system is automatically positioned to generate aninspection region that substantially overlaps with the identified targetregion. Where multiple threat locations are identified, the second stagescanning system is sequentially repositioned to focus on each subsequenttarget region. To scan each target region, the second stage X-ray sourceis activated and the scatter detector and transmission detector aresampled simultaneously. In a preferred embodiment, a transmissionspectrum associated with the detected transmission data is characterizedusing a look up reference, figure, table, or chart, and the scatterspectrum is normalized using that identified transmission spectrum.

In another mode of operation, an operator actively identifies imagesthat he or she believes corresponds to a potential threat. X-ray imagesfrom the first inspection stage are displayed to the operator, and theoperator points to a suspicious object as it appears in both views. Tosupport this functionality, operators use a computer system, comprisinga mouse and monitor, to position cross hairs over the areas of intereston each of the images. Using coordinate data generated throughtriangulation, the second stage scanning system automatically positionsitself such that an inspection region overlaps with the target region,activates the X-ray source and simultaneously samples the scatterdetector and transmission detector. In a preferred embodiment, atransmission spectrum associated with the detected transmission data ischaracterized using a look up reference, figure, table, or chart, andthe scatter spectrum is normalized using that identified transmissionspectrum.

As discussed above, a transmission detector is integrally formed withthe beam delivery system, as shown in FIGS. 5 and 6. A preferredtransmission detector comprises a 16 channel array of dual energydetectors. The detector array further comprises pairs of detectors,including a low energy channel that receives and measures a first amountof radiation first (low energy) and a high energy channel that receivesand measures a substantial portion of the balance of radiation (highenergy). Dual energy detection has been described in connection with thelinear scan arrays of the first inspection stage and is known to personsof ordinary skill in the art.

The low energy and high energy detectors measure a plurality of lowenergy and high energy values that can be used to characterize thematerial being scanned. In a preferred embodiment, low energy and highenergy data are used to reference a look up reference, figure, table, orchart (referred to as a look up source) which contains transmissionspectra arranged in accordance with corresponding high and low energyvalues. The look up source is constructed with high energy values on oneaxis (i.e. the x-axis), and low energy values on a second axis (i.e. they-axis). Referring to FIG. 7, an exemplary look up source 700 is shown.The source 700 is a graph with high energy values on the x-axis 705 andlow energy values on the y-axis 710. Points 715 corresponding tomeasured spectra 720 are positioned on the graph according to certainlinear combinations of the measured high and low dual energy detectorsignals on the x and y axis.

The transmission spectra used to normalize scatter data is thereforeidentified by obtaining high energy and low energy data values,identifying the point on the graph corresponding to the detected highand low energy values, and looking up the spectrum associated with thatpoint. Where the detected high and low energy values yield a point on agraph that corresponds to an intermediate point 730 proximate topre-established points 735, 715, a corresponding transmission spectra745 can be calculated by performing a two-dimensional interpolation ofthe spectra 740, 720 associated with the pre-established points 735,715.

To create the look up source, an exemplary approach places variousmaterials of known composition and thickness, exposes them to X-raysources, measures the resulting high and low energy data values, anduses the scatter detector to measure the corresponding transmissionspectrum. More specifically, the beam path of the beam delivery systemis modified to allow a direct beam from the focus through the pinhole tofall on the energy dispersive scatter detector. To further reduce thephoton flux into a range that can be tolerated for energy-dispersivemeasurement, the current of the X-ray source is preferably reduced by alarge factor, e.g. 100. Under these parameters, the scatter detector canbe used to measure the transmission spectrum. Materials of knowncomposition and thickness are placed in the beam path. The materials areexposed to X-ray radiation. Dual energy measurements are made using thedual energy detectors and a transmission spectrum is obtained using thescatter detector. Through this approach, for each material compositionand thickness, a transmission spectrum is obtained and correlated withdiscrete pairs of dual energy transmission detector readings. Thisinformation is then arranged on a chart with the high energy value ofthe dual energy detector measurement on the x-axis, and the low energyvalue on the y-axis.

It should be appreciated that, in the disclosed embodiment, the spectraare the looked-up objects of the look up source. Instead of the spectra,however, the look up source can alternatively consist of spectralattenuation functions related to the attenuation of the materials placedin the beam when the look up source is being generated. The spectrum canthen be obtained by multiplying one fixed spectrum, for example thespectrum measured without the material placed into the beam, with thespectral attenuation function retrieved from the look up source.Alternatively, the look-up source can contain numbers that are theparameters of analytical expressions, e.g. polynomials, which are formedto describe the attenuation functions in a parametric way.

The presently described approach is preferred because it enables theconstruction of a transmission detector array from lower cost materials,as opposed to constructing the array using more expensive energydispersive detectors and support electronics. Moreover, it alsoaddresses the difficult problem of using energy dispersive detectors tomeasure transmission spectra at the high flux rates that are experiencedat the location of the transmission detector in the given configurationand at the same time at which the scatter data are recorded. Therequired strong attenuation of the transmission beams is a difficultproblem that is avoided using the present invention. The look up tableis an important element because the preferred dual energy detectors usedin the transmission detector cannot deliver spectra directly.

Transmission spectra are being used to correct the scatter spectra thatare being recorded by the energy dispersive detector. Normalizingscatter spectra with transmission spectra corrects for the confoundingeffects introduced by the specific spectral distribution of the primaryradiation, as emitted from the X-ray source, as well as byspectrum-distorting effects known as beam hardening. To correct thescatter spectra, the detected scatter spectra are divided by thelooked-up transmission spectra.

A normalized scatter spectrum exhibits a plurality of features. A firstfeature is that the location of the peaks and valleys of the spectrumare determined by the molecular structure of the materials located inthe probe region. A second unrelated feature is that the averagespectral signal of the normalized scatter signal, which can be ofvarying intensity, is linearly related to the gravimetric density of thematerial in the probe region. This can be used for threat discriminationsince most explosives, particularly military explosives, have a densityrange above that of most other plastic or food items in suitcases.

In one embodiment, the normalized scatter signal is used to identify athreat item by comparing the obtained normalized scatter spectrum and/orspectral signal with a library of scatter signals from known threatitems. This comparison can occur automatically by using a processor tocompare a library of threat items, stored in a memory, with the obtainedscatter signals. Such a library is developed by measuring the normalizedscatter signatures of known threat items. In addition to using thetransmission detector to generate data used to identify referencespectra, the transmission detector can function in a plurality of otherways. In one embodiment, the transmission detector acts as a positionsensor. The transmission beam is interrupted or attenuated momentarilywhen an object on the conveyor crosses it. Tracking the moment ofinterruption can provide information on the physical position of thecontainer on the conveyor and be used to appropriately position the beamdelivery system or container.

In a second embodiment, the transmission detector array functions as animaging detector to provide precise attenuation data for certain areasin containers, like container wall areas, where contraband can behidden. When the circular beam is centered on an edge of a container,the edge of the container can be imaged in good detail, and can helpanalyze the edges for concealed threats.

In a third embodiment, transmission detector measurements can be used todetermine whether the inspection region is, in fact, the same targetregion previously identified in the first stage scan. If thetransmission data correlates with X-ray characteristics different thanthose obtained in the first stage scan, the relative positioning of thesecond stage scanning system and the object under inspection may bemodified until the transmission data correlates with the same materialcharacteristics that was identified in the first stage scan.

In a fourth embodiment, transmission detector data are also being usedto simplify the algorithm-training procedure of the system, as describedbelow, in particular the collection of threat material properties withirregularly shaped threat samples, like sticks of dynamite.

It should be noted that it would appear because the scatter radiationpath and transmission path differ downstream from the scatter volume,there would be inconsistencies in the data when scatter and transmissiondata are combined. This inconsistency is one example of a number ofpartial volume effects, solutions for which are addressed herein.However, the inconsistencies are not significant and can be toleratedwithout encountering significant performance degradation of the systemas a whole. As shown, FIG. 5 is not an isometric schematic and, inreality, the scatter angle is preferably about 3 degrees, and the realpath differences are comparatively smaller.

As previously discussed, the second stage scanning system positions aninspection region to physically coincide with the target regionidentified in the first stage scan. The positioning means may beachieved using any method known in the art. In one embodiment, aplurality of control commands is produced in response to thedetermination of the location of the target region. The control commandsare generated by at least one processor in data communication with aplurality of processors capable of executing the aforementionedtriangulation techniques and/or determining the intersection ofprojection lines to identify the location of the target region in threedimensional system coordinates.

The control commands comprise data signals that drive a three-axiscontrol system. The vertical position of the second-stage inspectionvolume can be adjusted to the target volume or region of the first stagescan by moving the conveyor system up or down. In another embodiment,the control commands comprise data signals that drive the adjustment ofthe beam delivery system in the second stage scanning system. The beamdelivery system adjustment can include any type of adjustment to thecollimation or beam focus, including the physical movement of aplurality of apertures horizontally, vertically, or diagonally, thephysical modification of the diameter of the ring aperture by, forexample, increasing or decreasing the aperture size. In anotherembodiment, the position of the support structure, or C-arm, can bemodified along the conveyor direction to appropriately position the beamdelivery system.

The second stage scan may be compromised when the volume of the targetregion is smaller than the inspection region of the second stage. Insuch cases, extraneous material, other than the material identified asbeing a potential threat, such as air, metal, or container edges, may beincluded. The resulting scatter radiation is therefore a function ofmultiple material types and may not be readily identifiable as being thesignature of a single substance.

In one embodiment, the present invention comprises a threat recognitionprocess that incorporates a training methodology which relies onlibraries in which threat signatures are obtained by combining thethreat with other common materials, such as clothing, plastic, air, andmetals. Specifically, the data used in training and developing thedetection process are chosen to include data, which are corrupted byerrors based on partial volume data from statistically varyingcontainers and threat and non-threat material combinations. When theinspection volume is partially filled with a threat substance andpartially filled with a second innocuous substance, a combination signalwill be detected by the second scanning stage. The automatic threatrecognition methodology recognizes the threat from the combinationsignal based upon the aforementioned training. An exemplary automaticthreat recognition methodology, based on neural networks, is describedin U.S. patent application Ser. No. 10/910,250 and is incorporatedherein by reference.

In a second embodiment, the detected scatter data is corrected for theeffects of extraneous materials by pre-processing the data. The motioncontrol system tracks where the inspection volume or region is locatedin relative to a specific reference point, such as the approximateoutlines of the container, and relative to the conveyor system. Becauseof the ability to measure and track these reference points, the amountand portion of the inspection volume occupied by the conveyor structurecan be determined. The conveyor structure includes the belt material aswell as the structural member that is underneath the conveyor, which isreferred to as the slider bed.

To correct the scatter spectrum for the presence of the conveyor in theinspection volume, the scatter spectrum of the conveyor materials ismeasured and stored in a reference database. When the scatter spectrumof the inspection region is detected and it is determined that theconveyor occupied a portion of the inspection region, the scatterspectrum is corrected by multiplying the conveyor material scatterspectrum by a weighting factor to account for the size of the inspectionvolume occupied and that amount is subtracted from the measurement.

Similarly, when part of the inspection volume is filled with air, as incases when suitcase walls are targeted by the inspection volume, it isknown that the contribution of the air-filled portion of the inspectionvolume to the scatter signal is approximately zero, and therefore,substantially all of the scatter signal can be attributed to thematerial in the remainder of the inspection volume. By accounting forthe air volume contribution, the characterization of the material in theremaining inspection volume is rendered more precise. Optical detectors,such as a plurality of light-curtains, can be positioned across andwithin the scanning system to generate control signals that conveyinformation about the height and edges of the container relative to theconveyor system and relative to the inspection region. It therefore canbe calculated which portion of the inspection region is filled with air.

In another embodiment, transmission values for the scatter beam aremeasured by an array detector. An exemplary array comprises 16 channelsand yields transmission data for 16 subdivisions within the inspectionvolume. The transmission values can be used to characterize the materialdistribution in the inspection volume. Based on these transmissionvalues, approximate mass values can be determined for masses containedin each of the 16 subdivisions. For example, where the transmissiondetector value returns a value indicating the subdivision has materialwith zero thickness, it can be assumed that the subdivision is occupiedby air.

In one embodiment, the inspection volume is subdivided. By reducing thesize of the inspection region, one can ensure that fewer differingmaterials occupy the same region and can therefore avoid the complexcomposite signals that get generated when multiple materials fill asingle inspection region. In one embodiment, system resolution isincreased by providing multiple energy dispersive detectors, such as 2,3, 4, 5, 6 or more, in place of a single energy dispersive detector asshown in FIG. 4.

Referring to FIG. 8, a schematic representation of the beam deliverysystem of FIG. 5 880 is shown relative to a beam delivery system havingmultiple energy dispersive detectors 885. A first system 880 comprisessingle detector 800 s, circular aperture 801 s, inspection volume 802 s,circular aperture 803 s, and X-ray focus 804 s. The dark areas representthe presence of radiation blocking material, e.g. ¼ inch lead alloy, andthe white areas represent areas that are transparent to X-rays abovekeV. A second system 885 comprises an X-ray focus 804 q, circularaperture 803 q, divided inspection volume 802 q, detector side beamshaping aperture 801 q, and quadruple detector 800 q. The aperture 801 qis center-symmetric and consists of four slits, each conforming to partof a circle. The centers of the circular slits are chosen to be of thesame pattern as the detectors of the quadruple detector 800 q. Forexample, if the detector cluster consists of four channels centered onthe four corners of a 2 by 2 mm square, the centers of the partial andcircular apertures lay on a circle with diameter equal to the squareroot of 2 times 2 mm. The resulting inspection region for eachindividual detection region is about one quarter of the full inspectionvolume. A subdivided inspection region provides a higher spatialresolution of the second stage inspection. Clusters of energy dispersivedetectors with their supporting electronics are commercially availablefrom companies such as eV Products, Saxonburg, Pa.

If more than one scatter detector is being employed, a collimatingsystem of vanes can be placed in front of the detector clusterorthogonal to the surface of the detector and in line with the plane ofseparation between each detector. Using a separator 805, diffractedradiation is more effectively limited to reach the appropriate channelin the cluster and, consequently, detected signals are more readilyassociated with materials from specific areas within the inspectionregion. The separator 805 extends from the surface of the detectorcluster toward the surface of the adjacent aperture. The number ofseparator vanes is dependent on the number of detectors. A typical vanematerial and thickness is lead alloy of 0.5 mm thickness.

Referring to FIG. 9, a flowchart summarizing the operational process ofone embodiment of the present invention is provided. A container entersinto the first stage scan 905 where it is exposed to a plurality ofprojected beams 915. From that exposure, X-ray characteristics aredetermined 920 and target regions containing potential threats areidentified 925, 935. If no potential threats are identified, thecontainer is not subjected to a second scanning stage 940. The threedimensional coordinates of the target region is determined 945 and,accordingly, the inspection region generated by the second stagescanning system is coordinated to coincide with the target region 950.The inspection region is subjected to X-ray radiation in order to obtaintransmission and spectral data 955. The spectral data is then analyzed960 to determine the existence of a threat. The data collected in thesecond stage scan comprises both localized dual energy transmission dataand localized BRAGG diffraction spectra, which are subject tostatistical variances, originating from photon signal fluctuations,partial volume limitations, or variations of the type of luggage andtheir contents, among other causes. As such, it is preferred to have aprocessing methodology that accounts for the fact that the raw data isnot sufficiently sensitive to detect threats with sufficiently low falsealarm rate.

Alternative First Stage Scanning System

Referring back to FIG. 1, a dual stage scanning system 100 comprisesconveyor systems 121, 122 for moving containers, baggage, luggage, orsimilar object 105 through a plurality of scanning stages 110, 115. Inthis alternative embodiment, dual stage X-ray scanning system 100comprises a Computed Tomography (CT) Unit as a first stage 110 and aSubstance-Identification Unit (S-I Unit) as a second stage 115. In anexemplary embodiment object 105 is, but is not limited to, a piece ofbaggage and will be described as such hereinafter. Baggage 105 movesthrough the two stages via conveyor systems 121, 122 in the direction ofarrow 125 (along the X-axis). Conveyor systems 121, 122 are controlledand coordinated by Luggage Transport Sub-systems (LTS) 141, 142,respectively, thus operating the combined system 100 at a high-dutycycle. Both the first stage and second stage further comprise computerprocessing systems 131 and 132, for respectively receiving andprocessing, CT (Computed Tomography) data signals and small angle X-raydiffraction spectra of a threat location. Optionally, a bypass conveyorbelt is provided between the first stage 110 and second stage scanningunits 115 that enables the object 105 to be passed through the scanningsystem without having to be first inspected by the second stage scanningunit 115. Such a bypass can be used if the first stage scanning unit 110indicates that no threat exists, or no suspicious region exists, in theobject 105 based on the first stage scan.

In one embodiment, first stage 110 is a CT unit, generating threedimensional (3D) imaging data, coded in gravimetric density. Computerprocessing system 131 of the first stage 1110 generates automatic imageanalysis resulting in, but not limited to, the approximate shape, size,density, weight and, location of potential threats. As the piece ofbaggage 105 is transported into second stage 115 via conveyor system 122along arrow 1125, the computer processing system 132 of the S-I Unitreceives a three dimensional coordinate map of the threats. Processingsystem 132 also receives the image volume file from the CT Unit viasuitable transmission links, such as, but not limited to an Ethernet LAN(Local Area Network) connection.

The S-I Unit subsequently interprets the three dimensional coordinatemap of threats and image volume data in second stage 115 and reacts bymoving its probing beams into the position best suited for sampling thethreat resolution information. In second stage 115, based upon itsautomatic threat resolution algorithm, the S-I Unit provides data to anoperator who can manually activate an alarm or clear an object, or,based on the data, the system can automatically clear the objectoractivate an alarm.

As mentioned above, first stage 1110 of the CT Unit of the presentinvention is preferably a conventional CT-scan system as is well knownto those of ordinary skill in the art. FIG. 12 is a depiction of aperspective tunnel view along the conveyor system of one embodiment ofthe present invention, and in particular, shows the functionalcomponents of CT Unit 1200 as employed in an exemplary embodiment offirst stage 1110. CT Unit 1200 comprises an annular shaped rotatingplatform or disk 1210 disposed within a gantry support 1220 for rotationabout a rotation axis that is preferably parallel to the conveyor anddirection of travel of baggage 1205. Rotating platform or disk 1210 isdriven about the rotation axis by any suitable drive mechanism, such asa combination of belt 1216 and motor drive system 1217, or any othersuitable drive mechanism as is well-known in the art. Rotating platform1210 defines a central aperture 1230 through which conveyor system 1235transports baggage 1205. CT system 1200 further includes an X-ray tube1240 and a detector array 1245 which are located on opposite sides ofplatform 1210.

As described earlier with reference to FIG. 1, CT Unit 1200 alsocomprises a computer processing system (not shown in FIG. 12) forreceiving and processing CT data signals generated by the detectorarray, and for generating the necessary command signals for operatingand controlling the Luggage Transport Sub-Systems (LTS) 141, 112. Thecomputer system preferably also includes a monitor (not shown) fordisplaying information including generated CT images.

In one embodiment, X-ray tube 1240 is controlled by a dual-energy X-raytube control system known to those of ordinary skill in the art. Dualenergy X-ray techniques for energy-selective reconstruction of X-ray CTimages are particularly useful in indicating a material's atomic numberin addition to indicating the material's density, although it is notintended that the present invention be limited to this type of controlsystem. While the present invention describes the details in connectionwith single-energy data, it should be understood that the description isapplicable to multiple-energy techniques as well.

In one embodiment, X-ray tube 1240 generates a preferably conical beam1242 of X-rays that pass through a three-dimensional imaging field,through which baggage 1205 is transported by the conveying system 1235.After the conical X-ray beam 1242 passes through baggage 1205transported through the imaging field, it is received by detector array1245, which in turn generates signals representative of the densities ofexposed portions of baggage 1205. Conical beam 1242 thus defines thescanning volume or imaging field. Platform 1210 rotates about itsrotation axis, thereby moving X-ray source 1240 and detector array 1245in circular trajectories around baggage 1205 as it is continuouslytransported through central aperture 1230 via conveyor system 1235, thusgenerating a plurality of projections at a corresponding plurality ofprojection angles.

Information from the detector array 1245 is subsequently sent to theprocessing system to determine the attenuation of the X-rays as theypass through baggage 1205. Using Conventional Tomography and threedimensional image construction methods, known to persons of ordinaryskill in the art, the attenuation information is used by the processorto compute a density for each voxel in a three-dimensional image of thebag 1205.

Voxels in a specified density range, which are physically adjacent inthree dimensions and have a density variation less than a predeterminedthreshold are grouped and assigned with a label for identification.Because this adjacency check is performed in three dimensions, thinregions of any shape in any orientation are readily identified. Further,the number of voxels in each region is determined and compared to athreshold. In an exemplary method of the preferred invention, smallregions are rejected as harmless; small regions are defined as thoseregions containing only a small number of voxels or a number of voxelsbelow a certain threshold. Large contiguous regions, that is, regionscontaining more voxels than a preset threshold, are identified assuspect. The mass contained in any suspect region(s) is then calculatedby multiplying the volume of each voxel in the region by its density. Ifthe resulting mass is greater than a preset threshold, for example, 1000grams, the region is tentatively identified as a threat region.

Additionally, by taking projections from at least two different angles,it is possible to triangulate the location of the potential threatrelative to the physical coordinates of the system. The triangulationprocess localizes items and/or areas that generate features of interestin the images and identifies their location in the form of systemcoordinates.

As is well known to those of ordinary skill in the art, thresholds aredetermined based on an extensive analysis of CT data, such as actualthree dimensional CT density data, for many actual threat and non-threatobjects. Exemplary thresholds include, but are not limited to, densitythresholds, mass thresholds, density-dependent mass thresholds, andprocess parameters used to carry out a tentative identification of athreat region. Any of such thresholds can be used as a basis todetermine whether detected characteristics of materials does, or doesnot, activate an alarm and/or warrant additional screening via a secondstage scan. The extensive analysis includes statistical analysis of thedata employing statistical methods such as simulated annealing andgenetic algorithms known in the art. This analysis allows for thresholdand/or parameter selection based on a particular objective to be met,e.g., false alarm and/or detection rate setting/optimization,discrimination of threat type, and other mechanisms.

The three dimensional image of baggage 1205 under inspection issubsequently presented to an operator for inspection over a suitablevideo device such as a monitor of the processing system. The threatregions tentatively identified at the first stage are preferably markedand/or tagged for resolution by an operator. If the operator determinesthat the threat(s) identified are innocuous she may dismiss thethreat(s) and clear the baggage without the need for further inspection.In such cases, the baggage or object under inspection may be permittedto continue via a bypass conveyor to the secured area, without having tofirst pass through the second stage scan. However, if the operator isnot able to resolve a threat, subsequent verification of the threatregion is then performed by the second stage. Alternatively, the systemcan be programmed to automatically require second stage scanning ifmeasurements of a region are determined to meet a first pre-definedplurality of values. Further alternatively, the system can be programmedto automatically send the object under inspection via a bypass conveyorto the secured area, without having to first pass through the secondstage scan if measurements of a region are determined to meet a secondpre-defined plurality of values

Referring back to FIG. 11, in order to verify the threat located infirst stage 1110 and preferably identify the threat substance, the datarequired by the S-I Unit in second stage 1115 from the first CT Unitstage 1110 comprise at least a threat map in three dimensions comprisingthe three dimensional coordinates of the potential threat identified bythe CT Unit in first stage 1110 and a three dimensional densitydistribution of the remainder of baggage 1105. In second stage 1115,computer processing system 1132, via the use of an algorithmsubsequently converts the threat map into a sequence of motion controlcommands, needed to line up the S-I Unit in second stage 1115 inspectionregions with the threat locations tagged by the first stage 1110, asfurther discussed below.

FIG. 13 is a flow diagram of one exemplary operational process of thedual stage scanning system of the present invention. In step 1310, apiece of baggage is transported via conveyor belt system to enter intothe first stage scan. In an exemplary embodiment, the first stage scanis a CT scanning system. In step 1315, the baggage is exposed to aplurality of projected beams from the CT scanner. From that exposure,X-ray characteristics are determined, in step 1320 and target regionscontaining potential threats are identified in step 1325. The CT Unitalgorithms reconstruct the volume density distribution and store a copyof the data file for the required documentation. If there is a laterneed, the stored data files can be inspected by an operator. If nopotential threats are identified, the container is not subjected to thesecond stage scan by the S-I Unit, as in step 1330.

If a potential threat alarm is triggered, the three dimensionalcoordinates of a target region is determined in step 1335. In step 1340,the inspection region generated by the second stage scanning system iscoordinated to coincide with the target region. The inspection region issubjected to small angle X-ray radiation in order to obtain Braggspectral data in step 1345. The spectral data is then analyzed, in step1350, to verify and determine the existence of a threat. In a preferredembodiment, the second stage scanning system also employs certain threedimensional baggage data adjacent to the threats. From this additionaldata, the second stage system (here, a S-I scanning unit) can calculatebeam hardening and spectral de-convolution functions for the actualdiffraction beam path. The functions are then used to correct themeasured diffraction spectrum, before it gets fed to a S-I Unitautomatic threat resolution algorithm. It should be noted that theautomatic threat resolution techniques described above can also beimplemented in the present embodiment.

In the interest of maximizing throughput, both the first stage CT Unitand second stage S-I Unit are combined in such a way that any bagcleared by the first stage, therefore not requiring second stageinspection, is transported via an alternate path along the conveyorsystem (essentially removed from the path of the second stage), toprevent a decrease in throughput. Referring back to FIG. 1, the primarypurpose of the LTS 141, 142 (collectively referred to hereinafter asLTS) is to handle all aspects of transporting luggage (such as baggagerouting and baggage positioning in the SIU gantry) through the system100, whether in a stand-alone or conveyor integrated (in-line) mode. TheLTS comprise conveyor systems 121, 122 along with associatedconventional motion control drives. The LTS is controlled andcoordinated by programmable controllers such as computer systems 131,132. As would be evident to persons of ordinary skill in the art,position sensors, positioning algorithm, detection algorithms, and othersources, like safety sensors, provide the input signals and commandsrequired by the LTS.

The LTS aims at achieving a plurality of objectives such as keepingtrack of baggage when it arrives at the desired destination, ensuringthat an alarmed bag can be made available for manual or second stageinspection at the earliest on-set of alarm, and keeping the inspectionpipeline optimally filled and running. Also, in order to achieveimproved throughput, both the first and second stages are preferablyoperated to be simultaneously active and do not have to “wait for eachother” to complete their respective scanning stages.

FIG. 14 is a flow diagram of the process flow of one embodiment of theluggage transportation subsystem (LTS), as described above. In step1405, the LTS receives instructions from an operator to start the scan.A piece of baggage is subjected to the first stage, CT Unit scan in step1410. After the bag has been transported through the first stage CtUnit, it is determined if further second stage inspection is required instep 1415. To achieve and maintain high levels of overall systemthroughput it is desirable to keep the number of alarms (generated inthe first stage) sent to second stage inspections within appropriatelimits. In one exemplary operational process, if a bag generates firststage alarms via use of the CT Unit, the LTS would require operatorintervention. The operator could override the numerous first stagealarms and direct the S-I Unit to inspect a lesser number of typicallocations in the second stage, after resolving other threat alarms basedon an inspection of any of the three dimensional image map of thebaggage generated in the first stage, manual inspection and/or othercontextual details. The limit of the number of first stage alarms beyondwhich the LTS calls for operator intervention is predetermined and basedupon past and real-time throughput data obtained from operating thecombined scanning system.

If no further inspection is required, the bag is moved out through asecond stage bypass in step 1445. If further inspection is required andthe second stage is occupied, baggage is parked on a parking conveyor ortransferred to a dedicate conveyor 1425. If further inspection isrequired and the second stage is not occupied, the baggage istransferred to the second stage conveyor in step 1435 and then out ofthe system upon scan completion 1420. This enables a quick turnaroundfor new baggage inspection in the first stage as well.

Also, while the first stage scans continually move baggage (at a certainspeed) additional time is required for processes such as scanned slicereconstruction, automatic threat detection, and threat localization.During this further processing, the baggage is moved out from the firststage portion of the system and awaits a decision on whether the secondstage scanning is required. If further scanning is required, the bagkeeps moving undisturbed and is subsequently transferred to the S-Iconveyor. The second stage conveyor is stopped at the leading threatlocation, enabling the S-I Unit signature or fingerprint to be obtainedwith the S-I unit gantry being simultaneously rotated to a properazimuth. Subsequent similar stops may be necessary depending upon thenumber of first stage alarms to be resolved/verified. After second stageinspection, the baggage is released.

Alternative Second Stage, or Individual Stage, Screening System

The present embodiment is designed to better detect objects that aremade from, but not limited to, special nuclear materials (“SNM”) and/orhigh atomic number materials. The system employs advanced imageprocessing techniques to analyze images of an object under inspection(“OUI”), which includes, but is not limited to baggage, parcels,vehicles and cargo and then alert the inspector, preferably with minimalhuman intervention, to the presence of these objects in the image. Theinspector is then provided with a visual indication in the image of thepresence, location, and configuration of the suspicious objects.

In one embodiment, the high-Z detection system of the present inventionis implemented as a first or second stage within existing X-ray baseddetection systems. Using high-Z detection capability as a method forclassifying high-Z regions of images enhances the throughput,detectability, and operational capability of current security screeningsystems.

In one embodiment, the present invention is directed towards a methodfor generating an image representation of high-atomic-number and specialnuclear materials within objects under inspection using a radiationsource, comprising generating an X-ray image using a radiographicinspection system; checking the image using an algorithm to clear orretain regions of objects based upon a threshold level; segmenting saidimage into regions based upon criteria; further inspecting regions thathave not been cleared by using said algorithm to determine their sizeand shape; comparing said regions to threat criteria; and issuing analarm to an inspector when a high-Z object is determined as suspiciousin said comparing step.

In one embodiment, the present invention is directed toward an imageanalysis system and method for automatically detecting objects withhigh-atomic-number (“high-Z”) materials or special nuclear materialthreats in radiographic images of baggage, parcels, and/or break bulkcargo without requiring additional imaging scans.

In one embodiment, the present invention is directed towards a methodfor generating both forward diffraction as well as fluorescence imagesof baggage, parcels, and/or break bulk cargo.

In one embodiment, the present invention is directed towards a methodand system for classifying objects in a generated image of an objectunder inspection, identifying suspicious areas that may be specialnuclear materials (SNM) or high-Z gamma-ray shielding, which couldconceal radioactive materials or radiological dispersal devices (i.e.“dirty bombs”).

In one embodiment, the present invention is directed towards an imageanalysis system and method for automatically detecting and classifyingobjects with high-atomic number (high-Z) materials or nuclear threats inradiographic images of vehicles and/or cargo, without requiringadditional image scans.

In another embodiment, the present invention is directed towards a highenergy portal X-ray inspection approach to enable a fast, accurate andefficient cargo scanning method, leading to increased threat detectionand vehicle throughput. The present invention is designed to detectobjects that are made from, but not limited to, special nuclearmaterials (“SNM”) or gamma-ray shielding materials used to concealradioactive materials or radiological dispersal devices (i.e. “dirtybombs”). The high-Z detection capability portal X-ray system is anenhanced radiographic system with improved image quality, image display,and automated image analysis.

In one embodiment, the portal X-ray inspection system of the presentinvention is deployed as a fixed (or stationary) system duringinspection, allowing for better reliability, increased availability, andlower acquisition and operational costs. The high energy portalinspection system allows for high penetration and resolution enablingthe effective and non-intrusive inspection of nearly all cargo,including dense loads.

In one embodiment, the high-Z detection system of the present inventionis integrated with existing detection systems. In one embodiment, boththe diffraction and fluorescence imaging stage are integrated as eithera first or second stage of a conventional dual stage scanning system.The high-Z detection method and system of the present invention can beadded to suitable X-ray imaging systems at low cost. In addition,multiple sources and/or detectors are not required on existing systems.The high-Z and special nuclear material detection and classificationcapability may be, in various alternative embodiments, incorporated intoexisting scanning systems, such as, but not limited to metal detectors,X-ray systems, baggage trace detectors, trace portals, personnelscanners, quadrupole resonance systems, X-ray diffraction systems, orpersonnel identification systems.

This high-Z detection process can be further generalized to accomplishthe detection of other threats that may be hidden in bulk cargo. Theseinclude explosives, firearms, and other weapons of mass destruction. Theuse of neural-network classifiers may be used to assign a statisticalprobability that the suspicious area is a threat.

In one embodiment of the high-Z detection methods and systems of thepresent invention, the image data are automatically processed and analarm given, for inspector resolution, if a high-Z material isdetermined to be present. Thus, it is not required that the inspectorperceive a suspicious object in the image. This approach iscomplimentary to existing passive portal detectors.

Although the embodiments are described below in the context of exemplarybaggage and cargo inspection system, it should be evident to persons ofordinary skill in the art that items other than luggage and cargo, suchas but not limited to packages, mail, and cargo-containers, or evenprocessed food stuffs, can also be analyzed and screened or graded andthat the descriptions are exemplary and are not restrictive of theinvention.

Reference will now be made in detail to specific embodiments of theinvention. While the invention will be described in conjunction withspecific embodiments, it is not intended to limit the invention to oneembodiment.

I. High-Z Material Detection in Baggage, Parcels, and Hold Baggage

In one embodiment, the present invention is directed toward an imageanalysis system and method for automatically detecting objects withhigh-atomic-number (“high-Z”) materials and/or special nuclear threatmaterials in radiographic images of baggage, parcels, and/or break bulkcargo without requiring additional imaging scans. In addition, thepresent invention is directed towards a method for generating bothforward diffraction as well as fluorescence images of baggage, parcels,and/or break bulk cargo. In one embodiment, the diffraction andfluorescence imaging stage is integrated as a first or second stage of aconventional dual stage scanning system.

The present invention is also directed towards a method and system forclassifying objects in a generated image of an object under inspectionand identifying suspicious areas that may be special nuclear materials(SNM) or high-Z gamma-ray shielding, which could conceal radioactivematerials or radiological dispersal devices (i.e. “dirty bombs”).

FIG. 1 is a schematic illustration of one embodiment of exemplarybaggage scanning system components of the present invention from both afunctional and an operational perspective. Preferably, but not limitedto such dimensions, the system of the present invention is designed suchthat it is able to handle suitcases, bags, parcels, and break bulk cargoup to 120 cm (length)×80 cm (width)×53 cm (height). When theconventional system finds an X-ray opaque (“high density”) object in abag, the system alarms, but no further information about the object isgiven. However, in one embodiment, the system of the present inventionis quantitative, displaying an estimate of the mass, density, atomicnumber, and even the type of explosive or narcotics threat during thescanning process.

Thus, the systems and methods of the present invention enable furthercharacterization of an opaque threat automatically by both declaringthat a high atomic number (“high-Z”) of special nuclear material ispresent and identifying the high-Z element or special nuclear materialitself. The system of the present invention includes both thediffraction X-ray stage and an energy-dispersive detector system.

Now referring to FIG. 11, the baggage scanning system of the presentinvention comprises fluorescence detector head 1105, which is mounted ina configuration that allows the recording of reflected X-ray spectrum1120. In one embodiment, reflected X-ray spectrum 1120 is thefluorescence (high-Z) x-ray signal path. While reflected X-ray spectrum1120 is being recorded, diffraction detector unit 1110 acquires adiffraction spectrum 1115 in the transmission direction. The X-rays thatare transmitted from the primary beam after passing through the objectunder inspection are detected by diffraction detector unit 1110.

High-Z materials containing substances such as, but not limited to lead,tungsten, tantalum, gold, platinum, uranium, and plutonium add theirdistinctive K fluorescence line emissions (fluorescence peaks) to thespectrum, as described in greater detail below. The energy offluorescence peaks of high-Z materials are high enough to be detectableoutside a suitcase that they are hidden in.

In the high-Z detection capable baggage inspection system of the presentinvention, a large C-arm 1125 moves the diffraction camera acrossconveyor 1135, forming one of three motion controlled axes to locallyaddress potential threats 1140 in object under inspection (“OUI”) 1145.In one embodiment, OUI 1145 is a piece of baggage. C-arm 1125 iscomprised of top section 1125 a, which is fixedly attached in aperpendicular fashion to vertical section 1125 b. Bottom section 1125 cis fixedly attached to vertical section 1125 b in a perpendicularfashion and is parallel to top section 1125 a. Diffraction detector1110, preferably a cadmium telluride detector, is located within topsection 1125 a of C-arm 1125. High brightness industrial X-ray tube 1150is located within bottom section 1125 c of C-arm 1125 and at leastpartially underneath conveyor 1135. By using an energy dispersivedetector/collimator system, the system is capable of using both theconventional X-ray diffraction function and the reflected fluorescencefunction to determine the nature of the high-Z material. Fluorescencedetector head 1105 is located within bottom section 1125 c of C-arm1125, adjacent to X-ray tube 1150.

FIG. 15 is a detailed illustration of one embodiment of a baggagescanning system of the present invention, further depicting the X-raytube and beam paths. Referring now to FIG. 15 both the primary beam path1510 a (and later the transmitted beam path) and reflected fluorescencebeam path 1510 are shown. Scanning system 1500 further comprises X-raysource 1505, which produces primary beam path 1530 to measure thetransmitted X-ray diffraction pattern and reflected fluorescence beampath 1510 to measure the fluorescence from a potential threat target1515 in an object under inspection 1520.

In one embodiment, as explained with respect to the prior embodiments,the detection system of the present invention operates automatically.Thus, the high-Z detection approach does not require that the inspectorperceive a suspicious object in the image. Instead, the image data areautomatically processed and an alarm given, for inspector resolution, ifa high-Z material is determined to be present. This approach can be usedas a compliment to existing passive radiation detectors.

In one threat detection system, such as in a dual stage scanning system,two projection scans of an object under inspection are taken. The scansare then analyzed for the presence of an explosive threat; if needed,the scans are also available for later alarm resolution by an operator.If a threat is suspected, the object under inspection proceeds on theconveyor to the second stage of the system where the diffractionspectrum at the threat location(s) determined in the first stage istaken. The spectra are automatically compared to the threat catalog, andan alarm is given when a match is found.

In one embodiment, the scanning system of the present inventioncomprises a fluorescence camera and high-Z threat alarm capability.Thus, the high-Z detection system of the present invention, is anenhanced radiographic system with improved image quality, image display,and automated image analysis. Using a high-Z detection methodology as amethod for classifying high-Z regions of images enhances the throughput,detection capacity, and operational capability of inspection systems. Assuch, it decreases scan and display time for the images to substantiallyshorter than six seconds. In addition, the target throughput for fullyautomated inspection plus operator clearance is approximately 160 bagsper hour.

In the first imaging stage, the system of the present inventionautomatically scans for the presence of highly attenuating metal parts.If detected, the object under inspection is automatically positioned inthe diffraction stage. In the scanning system of the present invention,the diffraction stage is the combined diffraction and fluorescencestage, in which both the diffraction and fluorescence spectra aredetermined. If the primary beam hits a high-Z material hidden in theparcel, the reflected X-ray spectrum, containing the fluorescencesignature of that target, will be recorded by the fluorescence detector.If the fluorescence spectrum contains a high-Z line, the systemindicates an alarm and the threat location for explosives and/or high-Zthreats are automatically indicated on the images.

In another embodiment, the scanning system of the present invention isin an operator interactive mode. Conventionally, in a dual stagescanning system, the operator can mark a location in the resultant X-rayimages, whereupon the system can automatically check that location forthe presence of a threat. With the added high-Z detection capability ofthe scanning system of the present invention, the operator can mark anylocation for testing for the presence of high-Z threat items.

As mentioned above, the fluorescent detection system of the presentinvention incorporates an energy dispersive detection system, which willreadily pick up a large range of radioactive emissions. High-Z materialswith an atomic number greater than 55 have fluorescence lines in therange of the energy dispersive detection system. Steel is a relativelylow Z (26) material and does not, therefore, show fluorescence lines inthe inspected energy range. The fluorescence signature is thusrecognized when the high-Z threat is physically hidden or camouflaged byany material typically found in objects under inspection, such as, butnot limited to baggage.

FIG. 16 is a table illustrating showing the K-shell fluorescence lineenergies in keV of a selection of different materials. Materials whichcan be reliably detected by the present invention, even in clutteredsituations as is common in transport parcels, are listed in the table.The fluorescence signal reflected from a high-atomic-number metal orcompound is very specific and thus, its spectral features are labeled as“simple”.

FIG. 17 is a graph depicting the “raw” fluorescence spectrum reflectedfrom a high-atomic-number metal or compound. As shown in FIG. 16, thespectrum resulting from a fluorescence signal is essentially a one ortwo line spectrum with a line position indicative of atomic number. Inthe case of when the object under inspection is a cluttered item, suchas baggage, however, the exciting radiation as well as the reflectedfluorescence radiation has to go through cluttering material, includingsuitcase walls and suitcase contents. As a consequence of the Comptonscatter from the cluttering material, the specific fluorescence signalis distorted or corrupted. If the cluttering material is of low and/ormedium atomic number (for example, iron), its fluorescence stays belowthe detection range of the system and will not be registered. The shapeof Compton scatter contribution to the line spectrum (in theconfiguration employed) is in principle well known to those of ordinaryskill in the art and will not be discussed in further detail here.

The system of the present invention identifies high-atomic-number(“high-Z”) materials, including, but not limited to those associatedwith weapons of mass destruction, such as special nuclear materials(SNM). The algorithm employed in the system is based upon, among othercharacteristics, the ratio of the attenuation to the size of objects,thereby providing a method for identifying high-Z materials. Thealgorithm automatically processes radiographic images of objects underinspection to identify suspicious objects with these characteristicsize-attenuation signatures of SNM.

The representative images used for detection in the scanning system ofthe present invention are, in part, obtained using a suitable industrialX-ray tube with the same distances and under similar scan conditions asconventional systems. Upon review of a database of over 2,000 images oflike objects under inspection, characteristic features are extractedcommon to a given type of object under inspection. For example, but notlimited to such example, a database may be based upon images of baggage.Characteristic features are then extracted based upon a common baggagetype. Typical categories include: household goods, consumer goods,electronic components, clothes/apparel, books/paper other commonpersonal, household, office items and various combinations of itemstypical of baggage, parcels, bulk break cargo or any other container aswould be evident to persons of ordinary skill in the art.

Representative images obtained with other inspection systems, such asbut not limited to gamma-ray (i.e. Co-60) and x-ray inspection systemsare also examined in order to develop a list of features thatcharacterize high-Z materials in these images. They are generallyannotated with a description of the contents of the container—forexample, some contain high-Z clutter, including PCs, laptops, PDAs,consumer electronics items and television Cathode Ray Tubes (CRTs), leadbatteries, and other household and/or office supplies/equipment. WhileCRTs are readily identifiable in the image due to their distinctiveshape, they will not be identified as suspicious high-Z objects by theimage analysis techniques of the present invention. The glass used toform a CRT contains about 10% lead oxide and it will not produce thecombination of attenuation, size, and other characteristics of specialnuclear materials or shielding. This determines the effect on theability to identify suspicious areas due to the penetration, resolution,dynamic range, and other operational parameters of these systems. Thishigh-Z detection capability can be used to process images from a varietyof inspection systems. The primary requirements are sufficientresolution to detect small quantities of high-Z materials and thepenetration to image through the surrounding clutter.

FIG. 18 is a graphical depiction of exemplary calibration curves foruranium, plutonium, lead, and steel relating material thickness to theattenuation (pixel) value. Thus, the attenuation measured in the image,described by the pixel value, is converted to a material thickness.These calibration curves are derived from measurements of theattenuation produced by steel step-wedges using an industrial X-ray tubeand can be used to illustrate how high-Z areas can be automaticallyidentified within an image.

For example, but not limited to such example, assuming a 2-kg mass of aspecial nuclear material, the corresponding volume of 100 cm³ (2-kg) isequivalent to a uranium sphere with a diameter of 58 mm. Thishypothetical uranium sphere correlates to a pixel value of about 11,000(shown on the graph using an upward pointing arrow), which furthercorresponds to a steel sphere of approximately 180 mm in diameter. Thisis shown on FIG. 18 as a right pointing and subsequently downwardpointing arrow. Thus, if this sphere is made up of uranium, then itwould have pixel attenuation values that are equivalent to approximately180 mm of steel. The size and resulting attenuation of the objectprovide a characteristic indication of high-Z materials. Therefore,objects in the image that have a lateral dimension of 60 mm and theequivalent attenuation of about 180 mm of steel are regarded assuspicious.

A similar situation exists for a sphere of delta-phase plutonium alloy(density of 15.9 g/cm³), as can be seen from the delta-Plutonium curvein FIG. 18. The discrimination problem is easier for low-Z cluttermaterials, such as plastics, where it would take a material thickness ofabout 19 times larger, i.e. 1100 mm to produce the same attenuation as2-kg of a special nuclear material. Due to their depth of penetration,however, high-energy x-ray inspection systems can easily detect aspecial nuclear material that is hidden within low-Z neutron shields.The high depth of penetration is a consequence of the high absorption ofX-rays and gamma rays by special nuclear materials, such as lead andtungsten, due to their high atomic number and density.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention. Forexample, while dual-stage scanning systems have been described withreference to first stage scanning systems comprising a CT scanningsystem and complimentary second stage S-I Unit scanning systems,comprising a transmission and scatter scan, other modifications andchanges can be made by those of ordinary skill in the art. Additionally,while many of the systems described herein have been described withrespect to use in dual stage scanning systems, it is to be understoodthat the embodiments described herein may be used as single stagescanning systems. Therefore, the present examples and embodiments are tobe considered as illustrative and not restrictive, and the invention maybe modified within the scope of the appended claims.

I claim:
 1. An inspection system comprising: a first inspection stagecomprising: a first X-ray scanner, wherein the first X-ray scannercomprises an X-ray tube having an extended spectral emission; a secondX-ray scanner wherein the first X-ray scanner and second X-ray scannerare positioned around an inspection volume, wherein the first X-rayscanner is positioned at a 7 o'clock position relative to saidinspection volume, wherein the second X-ray scanner is positioned at a 5o'clock position relative to said inspection volume, and wherein X-rayprojections from the first X-ray scanner and X-ray projections from thesecond X-ray scanner are mirrored relative to a central verticalscanning plane in said inspection volume, a detector array positionedaround the inspection volume and configured to generate image data;wherein the detector array comprises an array of stacked detectors,wherein a first detector of said stacked detectors is positioned todetect low energy X-ray photons emitted from one of the first X-rayscanner or second X-ray scanner and wherein a second detector of saidstacked detectors is positioned behind the first detector to detecthigher energy photons emitted from a same one of the first X-ray scanneror second X-ray scanner; a conveyor belt positioned with said inspectionvolume and configured to move an object being inspected through saidinspection volume; and a first processor coupled to said detector arrayand configured to receive said image data and generate an image volumefile of the object being inspected.
 2. The inspection system of claim 1wherein the detector array and first processor are configured togenerate image data coded in gravimetric density.
 3. The inspectionsystem of claim 2, wherein the first inspection stage further comprisesa sensor configured to determine when the object being inspected entersthe inspection volume of the first inspection stage; and a controllerconfigured to control an activation and deactivation of at least one ofthe first X-ray scanner and second X-ray scanner based on the sensorreading.
 4. The inspection system of claim 1 wherein the first processoris configured to execute an automatic image analysis to determine atleast one of an approximate shape, size, density, weight and location ofa potential threat within the object being inspected.
 5. The inspectionsystem of claim 1 wherein said detector array generates dual energy dataand wherein said first processor is configured to use said dual energydata to automatically discriminate between material having an atomicnumber of 13 and material having an atomic number of
 26. 6. Theinspection system of claim 1 wherein the detector array is configured inan L-shape around said inspection volume.